Refrigeration apparatus

ABSTRACT

In the case where one compressor that is operated by being connected in parallel is a compressor in which the discharged oil amount is small, and the other compressor is a compressor in which the discharged oil amount is large, the amounts of refrigerator oil in the compressors are made approximately equal. In the refrigeration apparatus in which an outdoor unit  100  includes at least two compressors, a first compressor  110  and a second compressor  120 , which are connected in parallel with each other; an oil separator  111, 121  is provided in a discharge pipe of each of the compressors  110  and  120 ; and a first oil separator  111  on the first compressor side is connected to a suction pipe  164  of the second compressor  120  via first oil return piping  114 , and a second oil separator  121  on the second compressor side is connected to a suction pipe  163  of the first compressor  110  via second oil return piping  124 , a rotary compressor is used as the first compressor  110 , and a scroll compressor is used as the second compressor  120 ; and an oil storage part  110   b  of the first compressor  110  is connected to the suction pipe  164  of the second compressor  120  via an oil guiding pipe  118.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on, and claims priority from, Japanese Application Serial Number JP2008-315651, filed Dec. 11, 2008, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a refrigeration apparatus that is provided with at least two compressors, a first compressor and a second compressor, which are connected in parallel, in an outdoor unit, and is suitable for large buildings such as office buildings and apartment houses. More particularly, it relates to a technique for making the amounts of a refrigerator oil in the compressors approximately equal.

BACKGROUND ART

For air-conditioning equipment for a large building such as an office building and an apartment house, a so-called multiple air conditioning system has been used in which a refrigerant is supplied from one outdoor unit to a plurality of indoor units installed in the building. In the large-scale system of this type, the outdoor unit is sometimes provided in plural numbers.

In the multiple air conditioning system, the required air cooling capacity or heating capacity differs depending on the number of operating indoor units. Therefore, to meet this condition, a plurality of compressors are mounted in the outdoor unit.

The case where two compressors are mounted is explained. Usually, as a first compressor, a variable-speed compressor in which the rotational speed is variable due to inverter control is used, and as a second compressor, a constant-speed compressor in which the rotational speed is constant is used.

Up to a predetermined capacity, the second compressor is not operated, and only the first compressor is operated with the rotational speed thereof being controlled by an inverter. In contrast, when a capacity higher than a predetermined value is required, the second compressor of constant-speed type is operated together with the first compressor.

Thus, in both of the case where only the first compressor is operated and the case where both of the first and second compressors are operated, the excess and deficiency of a refrigerator oil in the compressors must be prevented.

As one example of the preventive measures, in the invention described in Patent Document 1 (Japanese Patent Application Publication No. 2001-324230), the oil storage part of the first compressor and the suction pipe of the second compressor are connected to each other via oil return piping, and the oil storage part of the second compressor and the suction pipe of the first compressor are connected to each other via oil return piping.

According to the invention described in Patent Document 1, when both of the two compressors are operated, excess refrigerator oil is returned from the first compressor to the second compressor or from the second compressor to the first compressor, and when only one compressor is operated, excess refrigerator oil is returned to the own machine, so that a proper amount of refrigerator oil is held in the compressors.

However, if the discharged oil amount of refrigerator oil (the amount of refrigerator oil discharged together with discharged gas) differs between the compressors, the above-described conventional art cannot achieve the above-described effect in some cases.

For example, if it is assumed that the inverter controlled first compressor that is operated always is a rotary compressor, and the constant-speed second compressor that is operated when a predetermined or higher capacity is required is a scroll compressor, the discharged oil amount of the scroll compressor is larger, because of construction, than that of the rotary compressor.

The reason for this is as described below. In the rotary compressor, usually, a refrigerant compression section is disposed on the lower side of a motor, and the refrigerant gas generated in the refrigerant compression section passes through a passage or a gap present on the motor side and is discharged through a discharge pipe. Therefore, the refrigerant gas and the refrigerator oil are easily separated from each other. In contrast, in the scroll compressor, usually, the refrigerant compression section is disposed above the motor, so that even in an interior high pressure type, the refrigerant gas generated in the refrigerant compression section scarcely passes through the motor, and is discharged through a discharge pipe.

In the case where the amounts of refrigerator oil are deviated by the difference in discharged oil amount between compressors in this manner, the conventional art has a difficulty in solving this difference. In the worst case, oil runs short on account of the lowering of oil level, which may lead to a seizure accident. Even among the same rotary compressors, or among the same scroll compressors, the discharged oil amount may differ.

Accordingly, an object of the present invention is to provide a refrigeration apparatus in which the amounts of a refrigerator oil in compressors are made approximately equal even in the case where one compressor that is operated by being connected in parallel is a compressor in which the discharged oil amount is small and the other compressor is a compressor in which the discharged oil amount is large.

SUMMARY OF THE INVENTION

To achieve the above object, the present invention provides a refrigeration apparatus in which an outdoor unit includes at least two compressors, a first compressor and a second compressor, which are connected in parallel with each other; an oil separator is provided in a discharge pipe of each of the compressors; and a first oil separator on the first compressor side is connected to a suction pipe of the second compressor via first oil return piping, and a second oil separator on the second compressor side is connected to a suction pipe of the first compressor via second oil return piping, wherein the amount of discharged oil differs between the first compressor and the second compressor; and an oil storage part of the first compressor in which the amount of discharged oil is small is connected to the suction pipe of the second compressor in which the amount of discharged oil is large.

Preferably, a rotary compressor is used as the first compressor, and a scroll compressor is used as the second compressor.

According to the present invention, in the refrigeration apparatus in which the outdoor unit includes at least two compressors, the first compressor and the second compressor, which are connected in parallel with each other; the oil separator is provided in a discharge pipe of each of the compressors; and the first oil separator on the first compressor side is connected to the suction pipe of the second compressor via the first oil return piping, and the second oil separator on the second compressor side is connected to the suction pipe of the first compressor via the second oil return piping, the amount of discharged oil differs between the first compressor and the second compressor; and the oil storage part of the first compressor in which the amount of discharged oil is small is connected to the suction pipe of the second compressor in which the amount of discharged oil is large. Thereby, a refrigerator oil is supplied from the first compressor (for example, a rotary compressor) in which the refrigerator oil is present in a relatively large amount to the second compressor (for example, a scroll compressor) in which the amount of discharged oil is large via the oil guiding pipe. Therefore, the amounts of refrigerator oil in the compressors can be made approximately equal.

In the present invention, it is preferable that the suction pipe of the first compressor and the suction pipe of the second compressor communicate with each other; and the connecting position of the first oil return piping and the oil guiding pipe to the suction pipe of the second compressor be a position at which the refrigerator oil supplied from the first oil return piping and the oil guiding pipe to the second compressor side drops on account of the gravity and is sucked into the first compressor when the second compressor is in a non-operating state.

According to this configuration, when the second compressor is in a non-operating state, the refrigerator oil supplied from the first oil return piping and the oil guiding pipe to the second compressor side is sucked into the first compressor, and when the second compressor is in an operating state, the refrigerator oil supplied from the first oil return piping and the oil guiding pipe to the second compressor side is sucked into the second compressor as it is.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a refrigerant circuit diagram showing a general configuration of a refrigeration apparatus in accordance with an embodiment of the present invention; and

FIG. 2 is an enlarged view of a compressor section of an outdoor unit included in the refrigeration apparatus shown in FIG. 1.

DETAILED DESCRIPTION

A refrigeration apparatus in accordance with an embodiment of the present invention will now be described with reference to FIGS. 1 and 2. The present invention is not limited to this embodiment.

Referring to FIG. 1, this refrigeration apparatus includes an outdoor unit 100 and an indoor unit 200. The outdoor unit 100 includes a compression mechanism section 101, a four-way valve (directional control valve) 130, an outdoor heat exchanger 140 having an outdoor fan 141, an outdoor expansion valve 150, and an accumulator 160.

In the indoor unit 200, a plurality of (three in this example, for convenience of drawing the figure) indoor heat exchangers 210 each having an indoor expansion valve 211 are connected in parallel between liquid-side piping 11 and gas-side piping 12. Each of the indoor heat exchangers 210 is provided with an indoor fan, but the fan is omitted in the figure.

Referring to FIG. 2, according to this embodiment, the compression mechanism section 101 is provided with two compressors, a first compressor 110 and a second compressor 120 that are connected to discharge-side gas piping 13 in parallel.

In this embodiment, as the first compressor 110, a variable-speed type rotary compressor in which the rotational speed is variable due to inverter control is used, and as the second compressor 120, a constant-speed type scroll compressor in which the rotational speed is constant is used. The rotary compressor may be of a single rotor type, a usual twin rotor type, an injection system twin rotor type, or the like type.

A refrigerant discharge pipe 110 a of the first compressor 110 is connected to the discharge-side gas piping 13 via an oil separator 111 and a check valve 112. A refrigerant discharge pipe 120 a of the second compressor 120 is connected to the discharge-side gas piping 13 via an oil separator 121 and a check valve 122.

The oil separator 111, 121 separates a refrigerator oil contained in a high-pressure discharged gas refrigerant, and the check valve 112, 122 inhibits the high-pressure discharged gas refrigerant sent from the other compressor from entering the own compressor.

The accumulator 160 is provided on the refrigerant suction side of the compressors 110 and 120 to return the refrigerant that finished its work. From the accumulator 160, a main suction pipe 161 for a low-pressure refrigerant gas is led, and a branch pipe 162 is provided in the end part of the main suction pipe 161.

The branch pipe 162 is forked into two branches. One branch is connected with a suction pipe 163 for the first compressor 110, and the other branch is connected with a suction pipe 164 for the second compressor 120. In this embodiment, since the first compressor 110 is the rotary compressor requiring less liquid back amount, a sub accumulator 113 is provided on the suction side of the first compressor 110.

The oil separator 111 on the first compressor 110 side is connected to the suction pipe 164 for the second compressor 120 via oil return piping 114 having a capillary tube 115 serving as a pressure reducing means.

Similarly, the oil separator 121 on the second compressor 120 side is connected to the suction pipe 163 for the first compressor 110 via oil return piping 124 having a capillary tube 125 serving as a pressure reducing means.

Besides, in the present invention, an oil storage part 110 b of the first compressor (rotary compressor) 110 is connected to the suction pipe 164 of the second compressor (scroll compressor) 120 via an oil guiding pipe 116 including a capillary tube 117 serving as a pressure reducing means.

The connecting position of the oil return piping 114 and the oil guiding pipe 116 to the suction pipe 164 is a position at which the refrigerator oil supplied from the oil return piping 114 and the oil guiding pipe 116 to the second compressor 120 side can drop on account of the gravity. For example, in the case where the suction pipe 164 has a tilting part sloping downward toward the branch pipe 162 side, the oil return piping 114 and the oil guiding pipe 116 are connected to this tilting part.

According to this configuration, since the suction pipe 163 and the suction pipe 164 communicate with each other in the portion of the branch pipe 162, when the second compressor 120 is in a non-operating state, the refrigerator oil supplied from the oil return piping 114 and the oil guiding pipe 116 to the second compressor 120 side is sucked into the first compressor 110, and when the second compressor 120 is in an operating state, the refrigerator oil supplied from the oil return piping 114 and the oil guiding pipe 116 to the second compressor 120 side is sucked into the second compressor 120 directly.

Next, the operating action of this refrigeration apparatus is explained. When a capacity lower than a predetermined value is required, only the first compressor 110 is operated while the rotational speed thereof is controlled by an inverter with the second compressor 120 being in a non-operating state. In contrast, when a predetermined or higher capacity is required, the constant-speed second compressor 120 is operated together with the first compressor 110.

At the time of air cooling operation, the four-way valve 130 is switched over to a state indicated by solid lines in FIG. 1. Thereby, the gas refrigerant discharged from the compression mechanism section 101 is brought from the four-way valve 130 to the outdoor heat exchanger 140, being heat exchanged with the outside air, and is condensed (at the time of air cooling operation, the outdoor heat exchanger 140 acts as a condenser).

The liquid refrigerant condensed by the outdoor heat exchanger 140 passes through a check valve 151 connected in parallel to the outdoor expansion valve 150, and is supplied to the indoor unit 200.

On the indoor unit 200 side, the liquid refrigerant is decompressed to a predetermined pressure by the indoor expansion valve 211, and thereafter is heat exchanged with the indoor air by the indoor heat exchanger 210 to evaporate. Thereby, the indoor air is cooled (at the time of air cooling operation, the indoor heat exchanger 210 acts as an evaporator).

The gas refrigerant evaporated by the indoor heat exchanger 210 goes into the accumulator 160 via the four-way valve 130. After the liquid refrigerant has been separated, the gas refrigerant is returned to the compression mechanism section 101.

At the time of heating operation, the four-way valve 130 is switched over to a state indicated by chain lines in FIG. 1. Thereby, the gas refrigerant discharged from the compression mechanism section 101 is brought from the four-way valve 130 to the indoor heat exchanger 210, being heat exchanged with the indoor air, and is condensed. Thereby, the indoor air is warmed (at the time of air cooling operation, the indoor heat exchanger 210 acts as a condenser).

The liquid refrigerant condensed by the indoor heat exchanger 210 passes through the indoor expansion valve 211 the valve opening of which is controlled according to the heating capacity, and is supplied to the outdoor unit 100.

On the outdoor unit 100 side, the liquid refrigerant is decompressed to a predetermined pressure by the outdoor expansion valve 150, and thereafter is heat exchanged with the outside air by the outdoor heat exchanger 140 to evaporate (at the time of heating operation, the outdoor heat exchanger 140 acts as an evaporator).

The gas refrigerant evaporated by the outdoor heat exchanger 140 goes into the accumulator 160 via the four-way valve 130. After the liquid refrigerant has been separated, the gas refrigerant is returned to the compression mechanism section 101.

When both of the first and second compressors 110 and 120 are being operated, the refrigerator oil separated by the oil separator 111 on the first compressor 110 side and the refrigerator oil in the oil storage part 110 b of the first compressor 110 are supplied to the suction pipe 164 of the second compressor 120 via the oil return piping 114 and via the oil guiding pipe 116, respectively, and the refrigerator oil separated by the oil separator 121 on the second compressor 120 side is supplied to the suction pipe 163 of the first compressor 110 via the oil return piping 124. Thereby, the amounts of refrigerator oil in the compressors 110 and 120 are made approximately equal.

Comparing the rotary compressor of the first compressor 110 with the scroll compressor of the second compressor 120, the amount of refrigerator oil discharged together with high-pressure gas is larger in the scroll compressor than in the rotary compressor because of construction for the above-described reason. According to the present invention, however, excess refrigerator oil is supplied to the scroll compressor side of the second compressor 120 via the oil guiding pipe 116 from the rotary compressor side of the first compressor 110 to compensate the discharged oil, so that the deviation of the amounts of refrigerator oil caused by the difference in discharged oil amount between the compressors 110 and 120 can be solved.

When only the first compressor 110 is being operated, and the second compressor is not being operated, the refrigerator oil supplied from the oil return piping 114 and the oil guiding pipe 116 to the second compressor 120 side is sucked into the first compressor 110.

In the above-described embodiments, one first compressor (inverter-controlled rotary compressor) and one second compressor (constant-speed scroll compressor) are combined. However, even in the case where both of the first and second compressors are provided in plural numbers, the present invention can be applied.

Also, on condition that the discharged oil amount differs, both the two compressors may be compressors of the same compression type (for example, rotary compressors or scroll compressors). 

1. A refrigeration apparatus in which an outdoor unit includes at least two compressors, a first compressor and a second compressor, which are connected in parallel with each other; an oil separator is provided in a discharge pipe of each of the compressors; and a first oil separator on the first compressor side is connected to a suction pipe of the second compressor via first oil return piping, and a second oil separator on the second compressor side is connected to a suction pipe of the first compressor via second oil return piping, wherein the amount of discharged oil differs between the first compressor and the second compressor; and an oil storage part of the first compressor in which the amount of discharged oil is small is connected to the suction pipe of the second compressor in which the amount of discharged oil is large.
 2. The refrigeration apparatus according to claim 1, wherein the first compressor is a rotary compressor, and the second compressor is a scroll compressor.
 3. The refrigeration apparatus according to claim 1, wherein the suction pipe of the first compressor and the suction pipe of the second compressor communicate with each other; and the connecting position of the first oil return piping and the oil guiding pipe to the suction pipe of the second compressor is a position at which the refrigerator oil supplied from the first oil return piping and the oil guiding pipe to the second compressor side drops on account of the gravity and is sucked into the first compressor when the second compressor is in a non-operating state. 